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| 2. |
- Guo, Yong, et al.
(author)
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Deposition of droplets from the trachea or bronchus in the respiratory tract during exhalation : A steady-state numerical investigation
- 2020
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In: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 54:8, s. 869-879
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Journal article (peer-reviewed)abstract
- Respiratory droplets are bioaerosols that originate from the respiratory tract. Knowing their deposition characteristics during exhalation would facilitate the understanding of the source of large respiratory droplets and their importance in the spread of respiratory infectious diseases. In this study, computational fluid dynamics is used to simulate the motion and deposition of droplets released from either trachea or bronchi in a realistic reconstruction of the human respiratory tract. Influences of airflow structures and locations of droplet generation on droplet deposition are studied, and droplets with diameters between 1 and 50 mu m are examined. The deposition of droplets is found to be influenced mainly by the droplet diameter and the flow rate of exhalation. The number of droplets released from the trachea or bronchi that can escape into the environment decreases as the flow rate increases. When the flow rate is low (10 L/min), the critical diameter of droplets generated in the lower respiratory system that can escape into the air is approximately 12 mu m, but this diameter is approximately 5 mu m when the flow rate is medium (30 to 60 L/min) or large (90 L/min). The larynx is the dominant site of deposition for droplets smaller than the critical diameter, while trachea and bronchus are more important locations that account for the deposition of larger droplets. This study indicates that the lower respiratory tract is an important source of fine droplets (<5 mu m) in indoor environments, and larger droplets probably originate from the upper respiratory tract, which needs further investigation. Copyright
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| 3. |
- Peng, Lei, et al.
(author)
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Possible user-dependent CFD predictions of transitional flow in building ventilation
- 2016
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In: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 99, s. 130-141
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Journal article (peer-reviewed)abstract
- A modified backward-facing step flow with a large expansion ratio of five (5) was modeled by 19 teams without benchmark solutions or experimental data for validation in an ISHVAC-COBEE July 2015 Tianjin Workshop, entitled as "to predict low turbulent flow". Different computational fluid dynamics (CFD) codes/software, turbulence models, boundary conditions, numerical schemes and convergent criteria were adopted based on the own CFD experience of each participating team. The largest coefficient of variation is larger than 50% and the largest relative maximum difference of penetration length is larger than 150%. The predicted non-dimensional penetration lengths as a function of the Reynolds number (1-10,000) are found to be significantly diverse among different teams. Even when the same turbulence model or even the laminar model is used, the difference in the predicted results is still notable among different teams. It indicates that the combined effects of a lack of general turbulence model, and possible errors in multiple decisions based on users' experience may have caused the observed significant difference. Prediction of transitional flows, as often observed in building ventilation, is shown to be still a very challenging task. This calls for a solid approach of validation and uncertainty assessment in CFD "experiments". The users are recommended to follow an existing guideline of uncertainty assessment of CFD predictions to minimize the errors and uncertainties in the future.
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| 4. |
- Rich, Rebecca L., et al.
(author)
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A global benchmark study using affinity-based biosensors
- 2009
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In: Analytical Biochemistry. - : Elsevier BV. - 0003-2697 .- 1096-0309. ; 386:2, s. 194-216
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Journal article (peer-reviewed)abstract
- To explore the variability in biosensor studies, 150 participants from 20 countries were given the same protein samples and asked to determine kinetic rate constants for the interaction. We chose a protein system that was amenable to analysis using different biosensor platforms as well as by users of different expertise levels. The two proteins (a 50-kDa Fab and a 60-kDa glutathione S-transferase [GST] antigen) form a relatively high-affinity complex, so participants needed to optimize several experimental parameters, including ligand immobilization and regeneration conditions as well as analyte concentrations and injection/dissociation times. Although most participants collected binding responses that could be fit to yield kinetic parameters, the quality of a few data sets could have been improved by optimizing the assay design. Once these outliers were removed, the average reported affinity across the remaining panel of participants was 620 pM with a standard deviation of 980 pM. These results demonstrate that when this biosensor assay was designed and executed appropriately, the reported rate constants were consistent, and independent of which protein was immobilized and which biosensor was used.
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| 5. |
- Deng, Qihong, et al.
(author)
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Association between prenatal exposure to industrial air pollution and onset of early childhood ear infection in China
- 2017
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In: Atmospheric Environment. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1352-2310 .- 1873-2844. ; 157, s. 18-26
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Journal article (peer-reviewed)abstract
- Background: Otitis media (OM) is a common infection in early childhood with repeated attacks that lead to long-term complications and sequelae, but its etiology still remains unclear. Objective: To examine the association between early life exposure to air pollution and childhood OM, with the purpose of identifying critical windows of exposure and key components of air pollution in the development of OM. Methods: We conducted a prospective cohort study of 1617 children aged 3-4 years in Changsha, China (2011-2012). The prevalence of OM was assessed by a questionnaire administered by the parents. Individual exposures to nitrogen dioxide (NO2), sulfur dioxide (SO2) and particulate matter with an aerodynamic diameter <= 10 gm (PM10) during prenatal, postnatal, and current windows were estimated using the measured concentrations at monitoring stations. We used logistic regression model to examine the OM risk in terms of odds ratio (OR) and 95% confidence interval (CI) for exposure to different air pollutants during different timing windows, adjusting for covariates, multi-pollutants, and multi windows. Results: Life-time prevalence of doctor-diagnosed OM in preschool children in Changsha was 7.3%. Childhood OM was associated only with prenatal exposure to the industrial air pollution with adjusted OR (95% CI) = 1.44 (1.09-1.88) for a 27 g/m(3) increase in SO2, particularly during the first trimester of pregnancy. We further found that prenatal SO2 exposure was not associated with the repeated attacks but was associated with the onset of OM, adjusted OR (95% CI) = 1.47 (1.10-1.96). The association between prenatal SO2 exposure and early childhood OM was robust after adjusting for other pollutants and windows. Sensitivity analysis indicated that the association was stronger in females, children with parental atopy, and children living in houses with cockroaches, new redecoration, and condensation on window pane during winter. Conclusion: We provide new evidence that prenatal exposure to industrial air pollution is associated with early childhood OM in China and may contribute to the onset of childhood OM. Our findings are helpful in developing more effective preventative strategies for childhood OM. (C) 2017 Elsevier Ltd. All rights reserved.
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| 6. |
- Deng, Qihong, et al.
(author)
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Early life exposure to traffic-related air pollution and allergic rhinitis in preschool children
- 2016
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In: Respiratory Medicine. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 121, s. 67-73
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Journal article (peer-reviewed)abstract
- Background: Evidence linking long-term exposure to outdoor air pollution with allergic rhinitis (AR) in children is scare, and the role of components of air pollution and timing of exposure remains unclear. Objective: To assess the association of pre- and post-natal exposure to air pollution with life-time prevalence of AR in preschool children. Methods: We conducted a cohort study of 2598 children aged 3-6 years in Changsha, China. The lifetime prevalence of AR was assessed by a questionnaire administered by parents. Children's exposures to dioxide nitrogen (NO2), sulfur dioxide (SO2) and particulate matter with an aerodynamic diameter <= 10 mu m (PM10) during different pre-and post-natal timing windows were estimated using the measured concentrations at monitoring stations. The odds ratio (OR) and 95% confidence interval (CI) of childhood AR for exposure to different air pollutants during different timing windows were assessed by logistic regression model in terms of an interquartile range (IQR) increase in exposure level. Results: Life-time prevalence of AR in preschool children (7.3%) was associated with both pre-and postnatal exposure to traffic-related air pollution (TRAP), but only significant during the third trimester of pregnancy with adjusted OR = 1.40 (95% CI: 1.08-1.82) for a 15 mu g/m(3) increase in NO2 and during the first-year of life with adjusted OR = 1.36 (95% CI: 1.03-1.78) and 1.54 (95% CI: 1.07-2.21) respectively for 11 and 12 mu g/m(3) increase in NO2 and PM10. The association of early life exposure to TRAP with childhood AR was robust by adjusting for other air pollutants and timing windows. Sensitivity analysis indicated that the association was higher in the children who are male, young, with genetic predisposition by parental atopy, and living in damp houses. Conclusion: Early life exposure to traffic-related air pollutant during pregnancy and first-year of life may contribute to childhood AR.
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| 7. |
- Deng, Qihong, et al.
(author)
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Exposure to outdoor air pollution during trimesters of pregnancy and childhood asthma, allergic rhinitis, and eczema
- 2016
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In: Environmental Research. - : Elsevier BV. - 0013-9351 .- 1096-0953. ; 150, s. 119-127
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Journal article (peer-reviewed)abstract
- Background: Mounting evidence suggests that exposure to ambient air pollution is associated with the development of childhood allergic diseases, but the effect of prenatal exposure to air pollution on the risk of childhood asthma and allergy is unclear. Objectives: We evaluated the association between maternal exposure to outdoor air pollution during different trimesters of pregnancy and incidence of asthma, allergic rhinitis, and eczema in 2598 preschool children aged 3-6 years in China. Methods: Children's lifetime incidence of allergic diseases was obtained using questionnaire. Individual exposure to outdoor air pollutants during trimesters of pregnancy was estimated by an inverse distance weighted (IDW) method based on the measured concentrations at monitoring stations. We used multiple logistic regression method to estimate the odds ratio (OR) of asthma, allergic rhinitis, and eczema for per interquartile range (IQR) increase in the exposure to air pollutant in each trimester, which was adjusted for the effect of other air pollutants and its effect in other trimesters by a multi-pollutant/trimester model. Results: Incidence of asthma (6.8%), allergic rhinitis (7.3%), and eczema (28.6%) in children was associated with maternal exposure to traffic-related pollutant NO2 during entire pregnancy with OR (95% confidence interval [CID respectively 1.63 (0.99-2.70), 1.69 (1.03-2.77), and 1.37 (1.04-1.80). After adjustment for other pollutants and trimesters, we found the association was significant only in specific trimester: the first trimester for eczema (1.54, 1.14-2.09), the second trimester for asthma (1.72, 1.02-2.97), and the third trimester for allergic rhinitis (1.77, 1.09-2.89). Sensitivity analysis indicated that the trimester sensitive to the development of allergic diseases was stable. Conclusion: Maternal exposure to traffic-related air pollutant NO2 during pregnancy, especially in specific trimesters, is associated with an increased risk of developing asthma, rhinitis, and eczema in children. Our results support the hypothesis that childhood allergic diseases originate in fetal life and are triggered by traffic-related air pollution in sensitive trimesters.
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| 8. |
- Deng, Qihong, et al.
(author)
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Parental stress and air pollution increase childhood asthma in China
- 2018
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In: Environmental Research. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0013-9351 .- 1096-0953. ; 165, s. 23-31
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Journal article (peer-reviewed)abstract
- Background: Although air pollution and social stress may independently increase childhood asthma, little is known on their synergistic effect on asthma, particularly in China with high levels of stress and air pollution.Objectives: To examine associations between exposure to a combination of parental stress and air pollution and asthma prevalence in children.Methods: We conducted a cohort study of 2406 preschool children in Changsha (2011-2012). A questionnaire was used to collect children's lifetime prevalence of asthma and their parental stress. Parental socioeconomic and psychosocial stresses were respectively defined in terms of housing size and difficulty concentrating. Children's exposure to ambient air pollutants was estimated using concentrations measured at monitoring stations. Associations between exposure to parental stress and air pollution and childhood asthma were estimated by multiple logistic regression models using odds ratio (OR) and 95% confidence interval (CI).Results: Life time prevalence of asthma in preschool children (6.7%) was significantly associated with parental socioeconomic and psychosocial stresses with OR (95% CI) respectively 1.48 (1.02-2.16) and 1.64 (1.00-2.71). Asthma was also associated with exposure to air pollutants, with adjusted OR (95% CI) during prenatal and postnatal periods respectively 1.43 (1.10-1.86) and 1.35 (1.02-1.79) for SO2 and 1.61 (1.19-2.18) and 1.76 (1.19-2.61) for NO2. The association with air pollution was significant only in children exposed to high parental stress, the association with parental stress was significant only in children exposed to high air pollution, and the association was the strongest in children exposed to a combination of parental stress and air pollution. Sensitivity analysis showed that the synergistic effects of parental stress and air pollution on childhood asthma were stronger in boys.Conclusions: Parental stress and air pollution were synergistically associated with increased childhood asthma, indicating a common biological effect of parental stress and air pollution during both prenatal and postnatal periods.
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| 9. |
- Hang, Jian, et al.
(author)
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Age of air and air exchange efficiency in idealized city models
- 2009
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In: Building and Environment. - : Elsevier BV. - 0360-1323 .- 1873-684X. ; 44:8, s. 1714-1723
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Journal article (peer-reviewed)abstract
- Wind can provide relevantly clean external (rural) air into urban street network, i.e. city ventilation. The local mean age of air denotes the time it takes for the external air to reach a location after entering the urban canopy layer. The air exchange efficiency denotes the efficiency of flushing the street network with external air. However, difficulties exist in calculating the local mean age of air in a city due to open boundaries. The traditional experimental homogeneous emission method is adapted here in a CFD method to predict the urban local age of air and analyze the air exchange efficiency for city ventilation. Three simple city models are considered, including a round city model, a square city model and a long rectangular city with one main street parallel to the approaching wind or with two crossing streets. The difference in the city shape results in significant difference in the local mean age of air. In the round city of one narrow street, two inflows through street openings converge close to the city centre and exits through the street roof, so the air close to the city centre is relatively old and the air exchange efficiency is low (30%). For a round city with two crossing streets, a slightly non-parallel wind to the main street generates younger air and the higher air exchange efficiency in the city.
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| 10. |
- Hang, Jian, et al.
(author)
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Effect of urban morphology on wind condition in idealized city models
- 2009
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 43:4, s. 869-878
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Journal article (peer-reviewed)abstract
- Wind conditions in urban environments are important for a number Of reasons. They can serve to out of the urban environment and to moderate urban microclimatic conditions if transport air Pollutants satisfactory, yet can compromise pedestrian comfort and safety if not. We aim to study experimentally and numerically the effects of urban morphology (e.g., overall city form (skyline), street orientation, and street configuration) on wind conditions in cities. This report considers our initial investigations of two idealized city forms that are coincidentally similar to ancient Roman cities that were organized On One OF two primary streets - a main north-south street, the cardus maximus, and a secondary east-west street, the decumanus maximus - and contained within a well-defined perimeter. We first consider round and square city models with one main street set parallel to the approaching wind and a secondary street producing an intersection at city centre. Not Surprisingly, wind conditions in the two city models are dissimilar due to their shape differences. We then consider a long rectangular city model with a fully developed steady flow region along the main street. If the main street of the round city model is narrow, the parallel approaching wind cannot blow through the entire street and a penetrating inflow exists at the leeward opening. For the Found city model with two crossing streets, a slightly non-parallel wind to the main Street generates a stronger wind level in the entire street volume, Crown.
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